Now, since kernels “specify the spatial domain of an embryo,” kernels must designate different body plans. Although there are many gaps in our knowledge, as Davidson and Erwin remark, “There are a number of additional examples for which there is persuasive evidence for the existence of [genetic regulatory network] kernels awaiting discovery of the direct genomic regulatory code. Prospective examples include kernels common to all members of a given phylum or superphylum.” Therefore, because a crucial element of body plan development—the kernel—requires design, it is reasonable to consider body plans in general to be designed. So we can further conclude that design extends into life at least as far as animal phyla.
Of course, animals from different phyla share many features. For example, all animals are eukaryotes, and thus have cells with nuclei and a molecular skeleton. Nonetheless, recall the bicycle/motorcycle example I mentioned at the beginning of this chapter. Although the two-wheeled vehicles share some parts, it’s reasonable to view a motorcycle as a separate, integrated design. Following that reasoning, it seems likely that different phyla represent separate, integrated designs.
Does design extend further into life than phyla? Yes, very likely. A hallmark of animal development is the differentiation of cells into different types, such as muscle cells, skin cells, and retinal cells. Because of the medical importance of the immune system, excellent work has been done on how one type of immune cell, called a “B cell,” is formed. In the special issue of the Proceedings of the National Academy of Sciences that featured genetic regulatory networks, an article summarized B cell differentiation. Although work is tentative and is continuing, the number of protein factors known to be involved in the gene regulatory network for B cell differentiation is similar to the number involved in the endomesoderm kernel (about ten).36 The authors comment:
The B cell developmental pathway represents a leading system for the analysis of regulatory circuits that orchestrate cell fate specification and commitment…. [T]he proposed circuit architecture is foreshadowing design principles that include transient signaling inputs, self-sustaining positive feedback loops, and crossantagonism among alternate cell fate determinants.
Thus, because of its coherence and the number of its components (well beyond our criterion of three), it’s reasonable to think the system to specify B cell differentiation was also designed. B cells don’t occur in invertebrates; they are found only in vertebrates. Based on just this one particular example, then, it appears that design extends into the phylum Chordata, past the divide between invertebrates and vertebrates, which is the level of subphylum.
The work that goes into elucidating gene regulatory networks is enormous. At this point the B cell is one of the very few cell types where much is known about the gene networks that control its differentiation. However, if we assume that the B cell regulatory network is typical of what is needed to specify a cell type, we can conclude that design is required for new cell types in general. That will move us further along. Vertebrate classes differ in the number of cell types they have. Although amphibians have about 150 cell types and birds about 200, mammals have about 250.37 So, again keeping in mind the limitations of the data, because different classes of vertebrates need different numbers of cell types, we can tentatively conclude that design extends past vertebrates in general and into the major classes of vertebrates—amphibians, reptiles, fish, birds, and mammals.
Does design extend even further into life, into the orders or even families of vertebrate classes? To such creatures as bats, whales, and giraffes? Because “all of the structural characters of the edifice, from its overall form to minute aspects that determine its local functionalities…must be specified in the architect’s blueprints,”38 I would guess the answer is almost certainly yes. But at this point our reliable molecular data run out, so a reasonably firm answer will have to await further research. Given the pace of modern science, we shouldn’t have to wait too long.
BRACKETING THE EDGE
Does the reasoning above comport with what’s known from observational data? Yes. Let’s divide the answer into negative results and positive results. First, briefly, the negative. Of the many human genetic changes wrought by the struggle with malaria in the past ten thousand years, a few occur in regulatory regions. But nothing is built—single genes are simply shut down or deregulated; there are no new genetic regulatory systems formed. The same kind of small, incoherent changes we see in humans occur in other animal species, too. In a billion rats in the past fifty years, evo-devo theorists might expect many new regulatory regions; none seem to have helped against warfarin. In trillions of Antarctic notothenioid fish in the past ten million years, no new regulatory regions seem to have helped much in the fight against freezing water—only changes in protein sequences do. In the laboratory, the fruit fly has been studied in large numbers for over a century. Although its existing genetic control systems have been subjected to all manner of experimental insults, resulting in some bizarre birth defects, during that time no new, helpful, developmental-control programs have appeared.
The malarial parasite is a single-celled organism, so of course it does not need a body plan. Nonetheless, during its life cycle it changes between several distinct forms, which can be considered as akin to cell types. Yet in a hundred billion billion chances, no new cell forms or regulatory systems have been reported. What greater numbers of malaria can’t do, lesser numbers of large animals can’t do either. In other words, as expected, there is no evidence from our best evolutionary studies that random mutation leads to gene regulatory networks of the complexity of cell differentiation—that is, class-level biological distinctions.
On the positive side, some terrific work has been done in recent years yielding some persuasive evidence that random changes in existing control networks can helpfully affect animal form at the species level. One analysis that will warm the heart of any pet owner was an investigation of possible molecular reasons for the differences between breeds of dogs. A recent study adduced evidence that changes in some dog Hox genes, where one or several amino acid codons are repeated a varying number of times, are correlated with some differences in bone structure among breeds.39
A few other studies were highlighted in a recent issue of Science that designated “Evolution in Action” as the “Breakthrough of the Year.”40 One looked at the differences between two varieties of stickleback fish.41 It concluded that the ancestral form usually found in oceans, which has more bony armor in its body and three bony spines sticking up from its back, has given rise several times independently over the past few million years to a form usually found in fresh water, which has much less armor and fewer spines, probably due to mutations in certain control regions. Another study from the group led by Sean Carroll showed that males of a certain species in the genus Drosophila in the past 15 million years have gained a spot of color on their wings. The reason is that the gene for a pigmentation protein called Yellow protein (which actually produces dark pigmentation) has gained a new switch sequence for a particular regulatory protein.42 This result is important because it shows random mutation not only breaks switches, but occasionally makes new ones, too, just as it occasionally makes proteins with new functions such as the antifreeze protein of notothenioid fish.
These studies are great reminders that random mutation and natural selection can account for many relatively minor changes in life—not only changes in invisible metabolic pathways like antibiotic resistance in rats or malaria, but also changes in the appearance of animals. The different sizes and shapes of dogs, the patterns of coloration of insect wings, and more can very likely be attributed to Darwinian processes affecting gene switches.
Combining the reasoning from the past several sections, then, we can conclude that animal design probably extends into life at least as far as vertebrate classes, maybe deeper, and that random mutation likely explains differences at least up to the species level, perhaps somewhat beyond. Somewhere between the level of vertebrate speci
es and class lies the organismal edge of Darwinian evolution.
DARWIN AMONG THE SPANDRELS
So, given these results, if you are willing to consider the possibility of intelligent design, how should you view the relationship of Darwin to design? Although I’m sure they would disapprove, I think a felicitous image can be borrowed from a well-known paper by the late evolutionary biologist Stephen J. Gould and the Harvard geneticist Richard Lewontin entitled “The Spandrels of San Marco.”43 A spandrel is an architectural term that designates the “tapering triangular spaces formed by the intersection of two rounded arches at right angles.” As Gould later recounted, they co-opted the term “to designate the class of forms and spaces that arise as necessary byproducts of another decision in design, and not as adaptations for direct utility in themselves.”44 In other words, the joint between two designed structures has to look like something, but it’s a mistake to think the seam was necessarily intended for itself.
As an example of an architectural spandrel, Gould and Lewontin pointed to the “great central dome of St. Mark’s Cathedral in Venice.” Each of the four tapering spaces where rounded arches intersect in the cathedral is decorated with elaborate art, including a painting of one of the four evangelists. The painting fits so harmoniously with the cathedral, they wrote, that if you didn’t know better, you might think the whole structure was built just to give a space for the decorations. Yet the paintings, fitting as they may be, are merely filling an open niche. For similar reasons, the authors also pointed to the fan vaulted ceiling of King’s College Chapel of Cambridge University, where some open space along the midline is decorated with the Tudor rose. “In a sense,” they wrote, “this design represents an ‘adaptation,’ but the architectural constraint is clearly primary.”
And so it is between design and Darwin in life. The major architectural features of life—molecular machinery, cells, genetic circuitry, and probably more—are purposely designed. But the architectural constraints leave spandrels that can be filled with Darwinian adaptations. Of course, Darwinian processes would not produce anything so coherent as the paintings of the four evangelists. Random mutation and natural selection ornament biological spandrels more in the drip-painting style of the abstract American artist Jackson Pollock. The myriad gorgeous color patterns of animals—butterfly wings, tiger stripes, bright tropical fish—are some examples of Darwin among the spandrels.
Figure 9.4
A spandrel formed by two designed arches.(Drawing by Celeste Behe.)
Darwin decorates the spandrels. The cathedral is designed.
10
ALL THE WORLD’S A STAGE
CONSILIENCE
“Consilience” is an old-fashioned synonym for concurrence or coherence. When results from separate scientific disciplines all point in the same direction, we can be far more confident of the conclusion. About a decade ago the noted biologist E. O. Wilson wrote a book titled Consilience. Wilson argued that ideas from Darwinian evolutionary biology can illuminate other areas of knowledge, such as environmental policy, social science, and even the humanities. Because of this, he thinks he sees a consilience of results that supports what is variously called scientism, reductionism, or materialism—in other words, the view that the entire universe from the Big Bang to the Bolshoi Ballet can be explained by the random, unguided playing out of natural laws.
I think Wilson has it exactly backward. Rather than supporting randomness, a consilience of relatively recent results from various branches of physical science—physics, astronomy, chemistry, geology, molecular biology—actually points insistently toward purposeful design in the universe. In each case the results were unexpected and surprising. Merely intriguing when considered in isolation, when taken together the results from the disparate disciplines strongly reinforce each other. They paint a vivid picture of a universe in which design extends from the very foundations of nature deeply into life.
MINNESOTA FATS
Here’s a brief analogy to help think about the new consilience. Suppose in a small room you found a pool table, with all the pool balls held in one side pocket. Nothing much remarkable about that, you tell yourself. Now suppose you later discovered a videotape from an overhead camera, showing how the balls arrived in the pocket. As the tape begins, all the numbered pool balls are motionless, scattered on the table apparently at random. Then, in slow motion from one corner, the cue ball appears (you can’t see the cue stick or shooter—they’re off-camera). The cue ball hits a numbered ball, then another, which hits several others. After bouncing around a short while, all the balls line up and roll neatly, one after another, in numerical order, into the side pocket.
Even though you didn’t see what happened before the start of the film or off-camera, you would be certain it was a trick shot. No random cue stroke, that. It was set up—designed. The shot must have taken into account not only general laws of physics (conservation of momentum, friction, and so forth) but special conditions (the size of the table and mass of the balls) as well as minute details (the exact initial placement of the balls and angles of impact). Whoever set up the trick not only took care to select appropriate general conditions, including a smooth pool table, but also paid close attention to the smallest details necessary to make the trick work.
The pool table is our universe, and the consequence of all the balls in the side pocket is life on earth. The initial, static, naive view—the balls already in the pocket, where you first spot them—is akin to nineteenth-century science’s view of the universe. The jaw-dropping dynamic view given by the videotape is analogous to what modern science has discovered.
FINELY TUNED LAWS
In the second half of the nineteenth century the universe seemed pretty dull. It was thought to be eternal and largely unchanging, composed of relatively simple matter, obeying a few rules such as Newton’s law of gravity. Such a cosmos could have been mistaken for a background of boring wallpaper. In the most spectacularly wrong consensus in the history of science, in the words of two historians, “At the end of the nineteenth century there was a general feeling that, with Maxwell’s and Newton’s equations firmly established, everything else would be merely a matter of detail, a question of dotting the i’s and crossing the t’s of science.”1 As Yogi Berra observed, it’s tough to make predictions, especially about the future. Soon Einstein proposed his theory of relativity; quantum mechanics swept through physics; the atom was shown to be divisible—into protons, neutrons, and much more. Like the cell, which was also thought to be simple, the universe became more complex the more it was studied.
First the wallpaper was revealed to be full of strange details. Then the very size and shape of the room began to change. In 1929 the astronomer Edwin Hubble measured light coming from distant galaxies. He was startled to see that the wavelength of the light was somewhat longer than it should have been. The so-called “redshift” of starlight is similar to what happens when a speeding train, blowing its whistle, passes a person standing by the tracks, who hears the pitch of the whistle change from higher to lower as the train recedes. Hubble interpreted the redshift of starlight to mean that galaxies are rapidly receding from the earth and from each other, as if in the aftermath of a huge explosion. This was the beginning of the Big Bang theory, and the end of the humdrum, eternal, unchanging universe.
In the second half of the twentieth century physics advanced by leaps and bounds. More and more subatomic particles and forces were discovered, more and more measurements and computer calculations accumulated. In the mid-1970s a physicist named Brandon Carter paused to think about the new data from the viewpoint of what’s needed for life. In a paper entitled “Large Number Coincidences and the Anthropic Principle in Cosmology,” Carter pointed out that if any of a number of the multiple laws and constants that physics had discovered in the twentieth century had been a tiny bit different, the universe would be utterly unsuitable for life.2 In other words, the very same cosmos that appeared so bland just a hundred years ago now is
known to be balanced on a knife edge, with numerous factors arranged just-so, to permit life.
Since Carter’s seminal paper many commentators have remarked on the astounding “fine-tuning” in physics. Consider this oft-quoted passage from the physicist Paul Davies:
The numerical values that nature has assigned to the fundamental constants, such as the charge on the electron, the mass of the proton, and the Newtonian gravitational constant, may be mysterious, but they are crucially relevant to the structure of the universe that we perceive. As more and more physical systems, from nuclei to galaxies, have become better understood, scientists have begun to realize that many characteristics of these systems are remarkably sensitive to the precise values of the fundamental constants. Had nature opted for a slightly different set of numbers, the world would be a very different place. Probably we would not be here to see it.
More intriguing still, certain structures, such as solar-type stars, depend for their characteristic features on wildly improbable numerical accidents that combine together fundamental constants from distinct branches of physics. And when one goes on to study cosmology—the overall structure and evolution of the universe—incredulity mounts. Recent discoveries about the primeval cosmos oblige us to accept that the expanding universe has been set up in its motion with a cooperation of astonishing precision.3
Similarly, the Cambridge University physicist Stephen Hawking remarks:
The Edge of Evolution Page 22